Pattern contour tracing apparatus

ABSTRACT

Line or pattern edge contour tracing apparatus incorporating a triangularly shaped pair of photocells receiving either direct or pulsating light from the line or edge to be traced. The triangularly shaped photocell pair carried by a sensing head are arranged in overlapping positions across the line or edge to be traced and across the direction of sensing head movement to enable the entire area of each cell to be used in sensing line displacement or orientation. Providing successive pairs of triangularly shaped photocells arranged across the line or direction of travel and in circuits for combining their outputs provides resultant signals indicative of the deviation of the sensing head from the line or edge being traced with the output of the cells selected and combined dependent on whether an edge or line is traced and the tracing speed for controlling servo motors to drive the sensing head along the line or edge. In addition the output of selected cells are controlled to ensure the sensing head properly orients to the line when tracing at slow speed.

1 PATTERN CONTOUR TRACllNG APPARATUS [75] Inventor: Francis G. Bardwell,Elmhurst,1ll.

[73] Assignee: Stewart-Warner Corporation,

Chicago, 111. [22] Filed: Mar. 29, 1972 21 Appl. No.: 239,045

[51] llnt. Cl. G05d 1/00 [58] Field of Search 250/202, 203, 211;

[56] References Cited I UNITED STATES PATENTS 3,431,425 3/1969 Brown250/202 3,135,904, 6/1964 Purkhiser... 250/202 3,427,457 2/1969Domenico. 250/202 3,335,287 8/1967 Hargens 250/227 2,999,938 9/1961 IHann 250/202 3,609,373 9/1971 Desai 250/202 3,198,949 8/1965 Holdo250/202 3,069,550 12/1962 Neander 250/202 3,566,129 2/1971 Bardwe1l....250/202 3,610,935 10/1971 Von Voros 250/202 3,528,337 9/1970 Dulebohn250/202 Primary Examiner-James W. Lawrence Assistant ExaminerD. C. NelmsAtt0rneyAugustus G. Douvas et a1.

[57] ABSTRACT Line or pattern edge contour tracing apparatus incorporating a triangularly shaped pair of photocells receiving eitherdirect or pulsating light from the line or edge to be traced. Thetriangularly shaped photocell pair carried by a sensing head arearranged in overlapping positions across the line or edge to be tracedand across the direction of sensing head movement to enable the entirearea of each cell to be used in sensing line displacement ororientation. Providing successive .pairs of triangularly shapedphotocells arranged across the line or direction of travel and incircuits for combining their outputs provides resultant signalsindicative of the deviation of the sensing head from the line or edgebeing traced with the output of the cells se lected and combineddependent on whether an edge or line is traced and the tracing speed forcontrolling servo motors to drive the sensing head along the line oredge. In addition the output of selected cells are controlled to ensurethe sensing head properly orients to the line when tracing at slowspeed.

8 Claims, 5 Drawing Figures minimum 23 um I (5;, 7 6 7. 92 3 SHEET 1 OF3 PATTERN CONTOUR TRACING APPARATUS BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates in general to pattern contourtracing apparatus for controlling machine operation or the like, andmore particularly to a unique photocell and output arrangement forcontrolling the tracing apparatus and machine path to correspond to thepattern line or edge.

2. Description of the Prior Art Automatic pattern contour tracingapparatus incorpora'tes a sensing or steering head which carries aplurality of photocells together with a lamp for illuminating thepattern line or edge. Such apparatus is described in US. Pat. No.3,423,589, and a sensing head I for use in such apparatus is describedin US. Pat. No.

3,704,373, dated Nov. 28, 1972. In such apparatus the photocells sensethe position of the illuminated line or edge to controla steering servomotor, which rotates the head to maintain the cells angularly orientedrelative the line or edge and a pair of coordinate drive motors whichmaintain the head positioned over the line and drive. it in a desireddirection alongthe line, together with any cutting, sensing or weldingapparatus which is controlled to operate in accordance with the patterncontour represented by the line.

The photocells generallypresent a rectangular cross section to the lineor edge, image and are arranged on opposite sides of the line. Thiscreates a dead space bethe cells. By providing a plurality of pairs ofsuch cells in an array having overlapped spaced positions along the lineand by combining the outputs thereof together with the outputs of a pairof cells located on respective sides of the array, the sensing headcarrying the array is adapted for use in either fast or low speed linetracing or for use in edge tracing.

It is therefore an object of this invention to provide an improvedphotocell arrangement for use in either line or edge tracing.

It is a further object of this invention toprovide an array ofphotocells and combine the outputs thereof for use in either fast or lowspeed line tracing or edge tracing.

Other objects and advantages of this invention will be readily apparentfrom the following description together with the claims and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional largelyschematic view of a scanning head showing the illuminating, optical andphotosensitive means therein for scanning a pattern contour;

7 nal derived from the photocells illustrated in FIG. 2;

tween the cells in which a shift in the line or edge posi tion may notbe immediately detected.

Further, the width of the line limits theeffective area of thecell'providing useful signals. For example, a typical line is l/32 inchor 0.032inch wide. lf approximately one-half the line is seenby eachcell, each cell is effective to sense only 1/64 inch or only one-halfthe line width. Thus, as the line moves toward one cell or the other,one cell output increases while the otherdecreases. The signal outputsare generally, algebraically subtracted so that the ne'gative goingsignal of one cell is added to the positive going signal of the othercell until the line edge hits the dead space between the cells;whereafter, no further increase in signal is provided from one cell,while the output from the other cell shortly thereafter fails todecrease. The effect is to limit the effective change in signal fordisplacement of the line to substantially one-half the line width of1/64 inch. The effective cell dimension transverse to the line istherefore limited to-.l/32 inch since as soon as the line is seen byonly one cell, no signal change occurs and as the linemoves past thecell thesignal simply drops off.

SUMMARY OF THE INVENTION The present invention overcomes the foregoingproblem by employing a photocell pair arrangement having triangularlyshaped areas exposed to the line image with the area of each celloverlapping the other and the line along the line. The apexes of thetriangularly shaped areas face in opposite directions so that widechanges in the area of light on each cell occur in opposite directionsin response to deviation in the position of the line, while theoverlapped position of the-cells enables a signal change to occur inboth cells over the entire width of the line to therebydouble the lengthof the signal change and eliminate the dead spot between and FIGS. 4and4a illustrate the manner in which the outputs of an array of photocellssuch as illustrated in FIG. 2 are combined to provide line tracing atselected speeds or edge tracing.

DESCRIPTION OF THE PREFERRED EMBODIMENT .In FIG.,1 a portion of asteering head'or sensing head 10 also known as a scanning head, ortracer described in US. Pat. application Ser. No. 185,282, is shown inlargely schematic form. The head 10 is rotatable about an axis'l2 by-acoaxial steering servo motor M seen in FIG. 4 and is driven along apattern contour line such as line 14, which may be taken to representeither a drawing line or a pattern edge, by a pair of coordinate driveservo motors X and Y indicated in FIG. 4.

The servo motors X and Y drive the head 10 together with the machine tobe controlled in correspondence with the pattern in respectivedirections through respective lead screws, to provide a resultant headdirection indicated by arrow 16 corresponding to the se lected directionin which head 10 follows the line M or edge. The servo motors X and Yare controlled by a resolver R in accordance with a displacement errorsignal received by the resolver R from a photosensitive assembly 18carried by the head 10. The displacement signal is conventionallycombined by the resolver R with speed signals received over lead SSunder operator selection and in accordance with the resolver angularposition which is in turn controlled by the angular orientation signalvprovided by assembly 18 to the steering motor M to drive the X and Ymotors at respective speeds for following line 14 in the desireddirection.

sitive assembly 18 to produce an electrical output dependent upon theimage location to control the steering motor M and the X and Y motors.

A simplified form of photosensitive assembly 18 is shown in FlG. 2 andcomprises two photosensitive cells or areas 24 and 26. The area 24 is inthe shape of an isosceles triangle whose equal sides are parallel to andsubstantially coextensive with the respective hypotenuse of two righttriangles forming area 26 so that the apex of each triangle is locatedon opposite sides of line 14 whose center is indicated by arrow 16.Thus, each area is defined by edges diverging in opposite directions foroverlapping the line 14. The height of the triangles is defined by thelonger leg 28 of the right triangles forming area 26 and is arrangedperpendicular to the direction of travel indicated by arrow 16 so thatthe height of each triangle normally overlaps the line equally with thebase line 29 of each cell 24 and 26 located an equal distance from theline center and normally parallel to the direction of travel.

In this case the photosensitive areas 24 and 26 comprise photovoltaiccells which are appropriately separated along the adjacent legs;however, photoresistive cells may also be used. A conductive layer suchas silver or copper foil 30 is conventionally solder plated torespective surface portions of each cell 24 and 26 adjacent therespective base line and outside of the triangular areas, and a similarfoil (not shown) is plated to the opposite surface of each cell todevelop an appropriate output signal from each cell.

With the described pair of photosensitive cells 24 and 26 eachoverlapping the line 14, there is no dead space between the cells. Theline 14 is a drawing, it is normally l/32 inch or 0.032 inch wide andits center, indicated by arrow 16, normally bisects each triangular areaand the legs, including the legs 28. The height of each triangle alongleg 28 is three times the width of the line 14 so that each cell is 3/32inch or 0.120 inch wide with l/32 inch exposed on opposite sides of theline. Since the area of the cells 24 and 26 are equal and each isexposed to an equal amount of light, when the line 14 is centered, thetwo outputs combined provide a new output of zero at that time, as shownat 32 in FIG. 3. If the line 14 represents an edge, the edge image fallsalong a line corresponding to the center of line 14 indicated by arrow16 and again the area of one cell 24 exposed to light equals the areablocked in the other cell 26 by the pattern so that the combined signalsprovide a zero output indicated at 32 in FIG. 3. It will be appre ciatedthat the signals may be added together and subtracted from a referencesignal or otherwise combined.

As the line 14 moves to the right, for example, the output of cell 24linearly increases, while the output of cell 26 linearly decreases toprovide a positively swinging signal output indicated at 34 in FIG. 3for application to the steering motor M, the resolver R and the X and Ymotors for controlling the head accordingly. Similarly, if the line 14moves to the left or clockwise, the output of cell 24 linearlydecreases, while cell 26 increases to provide a negatively swingingimpulse as indicated at 36 in H0. 3 for application to the motors M, Xand Y for aligning the head 10 with the line. Since the cells 24 and 26are each affected by movement of the line or edge along the entirelength of leg 28, the output signals 34 and 36 are provided for amovement of the line equal to leg 28 minus the width W of line 14. Thus,the signal output changes in each direction 34 or 36 over one-half ofleg 28 minus the line width of (L- W)/2; whereafter, if the line startsto move off the sensitive cell area, the signal falls as indicated at 38in FIG. 3. If the center of line 14 represents a pattern edge, aslightly greater signal range is obviously provided. Thus, the availablesignal change is substantially greater than the signal change availableif the cells are aligned side by side or on opposite sides of the linecenter represented by arrow 16.

Referring now to FIG. 4, a practical photocell assembly for use with ahigh speed tracer of the type described in the aforementionedapplication is indicated therein by the reference character 18. Theassembly 18 comprises a plurality of pairs of photosensitive orphotovoltaic equal area cells identified as A and B, C and D, E and Farranged as described for cells 24 and 26. The cells A-F are carried bythe head 10 in a stacked coplanar array with one cell of each pair beingan isosceles triangle and the other cell arranged as a pair of righttriangles with each hypotenuse adjacent but separated from a respectiveleg of the isosceles triangle. Legs 28 corresponding to the height ofeach triangular area are arranged perpendicular to the theoreticaldirection of head travel indicated by arrow 16. The head 10 is either orboth rotated or moved in the X and Y direction to align the direction oftravel 16 with the line 14 in response to so-called error signals fromthe cells. The actual axis of rotation of the head 10 lies along a lineintermediate cells A and C and offset from line 14 by a distancecorresponding to the kerf adjustment. Thus, axis 42 lies intermediatecells A and C on a line corresponding to line 14bisecting the area andlegs of each triangle with the base legs of the triangle arrangedparallel to line 14. Thus, with the head 10 traveling in direction 16,cells E, F, C and D sense a change in direction of line 14 with cells Aand B.

In addition, rectangular photosensitive or photovoltaic cell G or Hequal in area to cells A or B for sensing are arranged adjacent arespective base line of cells A and B, with the cells G and H extendingfrom a position coincident with the initiation of cell A to a positionadjacent the adjacent ends of cells D and E.

A foil electrode is provided along a small area adjacent the base lineof each triangular area and a small portion of rectangular cells G and Hto permit the connection of a respective lead from each cell to arespective preamplifier APHP. Electrodes at the opposite cell surfacesare connected in common or to ground. Leads Al H1 extend from respectivepreamplifiers AP-HP to conventional summing networks AB, ABl, AC, AD,AF, BC, BD, BE, CD and GH with the letters identifying each networkserving to identify the cell feeding the network. The summing networks,as for example explained in the aforementioned patent, serve to add thecell output signals although they can also be subtracted.

The outputs of the summing networks AB-GH are applied to respectiveconventional difference amplifiers indicated at AB-GH, AB-CD, AC-BD,AD-BC and AF-BE, which amplify the respective differences in signallevel between the summing networks with the letters identifying thecombined cell outputs. The output from the respective differenceamplifiers ABGH.- ..AFBE are applied over respective leads throughrespective conventional demodulators, detectors and amplifiers toconventional FET circuits Fde-Frh.

The FET circuits Fde and Fdel are fed by amplifier AB-GH and in turnfeed the displacement edge lead de and line or edge start lead df,respectively. The FET circuits Pd] and Fdle are fed by amplifier AC-BDand in turn feed the displacement line lead d1 and the edge start leaddf, respectively. The FET circuits Frl, Frh, and Fre are fed byamplifiers AD-BD, AF-BE and AB-CD, respectively, and in turn feed lowrotation lead r1, high rotation lead rh and edge rotation lead re,respectively, which in turn are applied through a resistor network R1and R2, an amplifier AM and contacts RS1 of a start relay RS to thesteering motor M of the sensing head 10.

The displacement edge lead de and displacement line lead d1 extend tothe resolver R through contacts RS4 of the start relay RS, which alsoconnects the resolver output to motors X and Y through respectiveamplifiers at contacts RS2 and RS3. The start lead df feeds the startrelay RS through an amplifier to initially sense the line or edge,respectively. Relay RS also controls contacts RS5 to start the cuttingapparatus which is to cut a pattern corresponding tothe edge or line 14.

It will be appreciated that additional circuits such as those for thelamps, filter and detector circuits and for operating themotors directlyunder the control of the operator are not shown and that the relaycontact and amplifier arrangement may be varied from that shown sincethese are conventional. p

The FET circuits operate as switches and analog ar'nplifiers and areselected by the operator in accordance with the mode, of operation.Thus, if theste ering head the operator renders Fde'and Fdle effectivetogether with Fre..Since tracing of an edge is generally carried out ata single speed range, there is no need to provide a speed selection forthis mode of operatiomThe gain reduction network R1 and R2 is used onlyto find the line'14 when tracing at low speed and is rendered effectiveby the operator at lead RG.

Thus, assuming it is desired to trace line 14 representing a drawing ata relatively low speed, the operator sets the kerf adjustment, selectsFET circuits Fdl and Fdel together with Frl and selects appropriatespeeds for the X, Y coordinate motors. He also operates the lamp 20 andthe conventional switches to drive the head 10 towards the line 14 withthe head oriented towards line 14 and direction 16 by appropriateoperation of the X and Y motors, or he manually moves the head 10 overthe line 14 while orienting the head in the tracing direction 16. Ifdesired, he also renders the gain reduction network R1 and R2 effectiveby operating switch RX to place a suitable shunt on lead RG and reducethe output applied to the. steering motor M through amplifier AM.

As the head 10 approaches the line 14, which for example may beinitially oriented asv indicated by broken lines 44 relative thedirection of actual head movement indicated by arrow 45, the photocell Ginitially senses the line. The output of cell G falls to reducethesignal level from network GH and provide a positive going signal fromamplifier AB-GH, which is applied to lead df, but blocked from the startrelay RS by rectifier DR. As the head 10 continues, it approaches closerto the line as is indicated by line 46. The light intensity falling oncell G is increased since the line image no longer falls on it, and cellG provides a corresponding output on lead G1 which is algebraicallyadded to the output of cell H at summing network GH to thereby provide alarge signal output to difference amplifier AB-GH which is subtractedfrom the signal provided by cells A and B to network AB. Since the linefalls on cells A, the output signal of cells A and B at this time fromnetwork AB is low and amplifier AB-GH provides a large negative goingsignal from Fdel to lead df for operating relay RS.

Relay RS closes contacts RS1 to connect the output of Frl to thesteering motor M, contacts RS4 to connect the output of Fdl to theresolver R, contacts RS2 and RS3 to connect the resolver output to thecoordinate motors X and Y and contacts RS5 to initiate the welding orcutting operation to be controlled in accordance with the patterncontour represented by edge or line 14.

The signal on leads rh and dl-is now connected to steering motor M andresolver R, respectively, as motors X and Y move the cells A and C overthe line as indicated at 46. The reduction in light on cells A and Ccreates a change in signal output from network AC, while similarsignal-changes are provided by summing networks AD and BC, sincethe'cells B and D sense more light at this time than cells A andC. Thedifference amplifier AC-BD, therefore, provides an error displacementsignal representing the difference in light seen by B and. Dover thatseen by cells A and C for applicationto 'Fdl over lead d1 to theresolver R to operate the X and Y motors for driving head 10 toward theline..

. In the meantime, with line 14 positioned as indicated at 46, cell Csees considerably less light than cell D, while cell A also sees lesslight than cell B, the total light seen by A+D is greater than that seenby B+C. The output of network BC, therefore, becomes unbalanced relativenetwork AD and amplifier AD-BC supplies a corresponding output throughnetwork R1 and R2 to the steering motor M. Motor M now rotates the headcounterclockwise relative axis 42 which tends to orient the arrow 16perpendicular to the line. This counterclockwise direction at this timeis opposite to that in which the head would normally orient if the linewere centered on the axis 42. Normally the reaction of motor M takesplace quite rapidly, and the steering head motor M may rotate the headin a counterclockwise direction. To avoid this situation, the gainreduction network lead RG is rendered effective by operation of switchRX to reduce the signal supplied by amplifier AM to motorM when findingthe line at low speed. The motor M will then operate slowly, while the Xand Y motors are operating to bring the line over cells A and B throughthe displacement amplifier AC-BD to. ensure normal centering of the line14 in the direction 16 on axis 42. As the head 10 proceeds towards theline now indicated at 48, the line image falls on all the cells A, B, Cand D and cell D senses less light than cell C in accordance with theposition of line 48 while cell A senses less light than cell B. Thesteering motor M receives a signal of corresponding orientation fromamplifier AD-BC which is opposite that previously received and starts torotate the head 10 clockwise relative axis 42 to align arrow 16 parallelto line 48 and thereby equalize the light sensed by cells A and C. Asthe head 10 centers axis 42 over the line 14,

which may be located at 14, the output of cells A and C equalizes withcells B and D to control the output of amplifier AC-BD accordingly. Theoutput of amplifier AC-BD applied to the resolver R through Fde controlsmotors X and Y accordingly so that the head 10 moves along the line 14in the direction 16 with the direction 16 being the resultant of thevector movement provided by motors X and Y. The operator notes theautomatic head movement and renders lead RG ineffective. The gain ofamplifier AM is restored to normal and the steering motor M maintainsthe head 10 angularly oriented on the line in response to the differencein light sensed by cells A and C or B and D, as explained, and controlsthe resolver output accordingly.

If the head 10 approaches the line 14 in the opposite direction, cellsH, B and D sense the line first; however, the principles of operationremain the same. If the head were manually moved approximately over theline and faced in the direction of movement, the relay RS is operated,since the signal level at cells A and B is less than G and H and thecenter of the line is found by head 10 by the displacement error signalprovided by amplifier AC-BD and the rotational error signal provided byamplifier AD-BC.

As th head 10 moves along the line 14, any angular deviation in the linecreates a signal difference between cells A+D compared with cells B+C atamplifier AD-BC for operating the motor M in the appropriate direction.When the line 14 curves, as indicated at 50 for example, the portion 50will be sensed first by a disturbance in the light balance received bycells C and D with either one or the other receiving greater light andthe other less light to alter the output of networks AD and BCaccordingly. This output varies the output of amplifier AD-BC in adirection corresponding to the line deviation for in turn rotating thesteering motor M to rotate the head 10 for maintaining the headangularly oriented with the line and controlling the resolver output tomotors X and Y for following the line. Displacement of the line relativethe axis 42, as explained, creates an unbalance in the output of cells Aand C relative cells B and D so that the resulting output of amplifierAC-BD is fed through the resolver R to control the X and Y motors tocompensate for the displacement.

If the line 14 is to be traced at high speed of, for example lZO inchesper minute, the FET circuit Frh is rendered effective instead of Frl. Inaddition, circuit Fdl and circuit Fdel are rendered effective to operatethe X and Y motors as soon as relay RS is operated in response tosensing the line 14, as previously explained. The gain reduction networklead RG is not used in this case since the X and Y motors are operatedat a substantially higher speed so that cells A, B, E and F are over theline before the steering motor M can rotate the head too far in thewrong direction. Cells E and F are not effective at amplifier AF-BE inplace of cells C and D for sensing rotation while cells C and D are onlyused for displacement signals at amplifier AC-BD.

The signal developed by cells A and C compared with the signal fromcells B and D at networks AC and BD provides a displacement error signalfrom amplifier AC-BD to drive the motors X and Y for moving the headinto alignment with line 14. It is therefore unnecessary to use the gaincontrol lead RG at high speed scanning. Since the motor speed is high,the steering head 10 does not have a chance to turn perpendicular to theline during the time the relay RS is rendered operative and the time theimage falls totally on the cells, especially since the relay takes timeto turn on.

Thus, cells A and B together with cells G or H sense the line positionunder head 10 to operate relay RS as previously explained, which in turnconnects the output of lead Frh to the steering motor M, and the outputof Fdl to the resolver R for controlling the X and Y motors to centeraxis 42 over the line. If cell E now senses less light than cell A, theoutput of network BE is less than network AP to provide a change inoutput signal at amplifier AF-BE. Amplifier AF-BE in turn applies thissignal difference over lead rh to the steering motor M to rotate thehead 10 counterclockwise for aligning the head with the line. If thesignal appearing at network AF is less than network BE, on the otherhand, the steering motor M is operated in the clockwise directionrelative axis 42 to correct for the angular misalignment between axis 42and the line.

Since cells E and F are displaced from axis 42 by a distancecorresponding to the dimensions of cells C and D along the line, thesteering motor M receives a signal from amplifier AF-BE in the event theline curves, as shown at 50, some distance prior to the alignment ofportion with axis 42. The steering motor M therefore rotates the headtoward portion 50 to align the direction of head movement 16 withportion 50 before the arrival of axis 42 at portion 50 to therebyovercome any tendency of the head to overshoot the line, while the X andY motors arev operating at high speed. The scanning of the line 14 fordisplacement proceeds as described for low speed line tracing with theexception that cells E and F are used to determine angular orientationas already mentioned.

For edge tracing the FET circuits Fdle, Fde and Fre are activated by theoperator, while the X and Y motors are operated by the operator to drivethe steering head 10 toward the edge, which may thereafter occupypositions corresponding to that shown for lines 44 or 46. Cells G or Hwill first sense the edge and the output of that cell will fallaccordingly; but the start relay RS does not operate until Fdle recievesan output from amplifier AC-BD resulting from a fall in light sensed bycells A or C or B or D, depending on the direction in which the headapproaches the edge. Assuming then that the head approaches the patternedge to cause cells A or C or both to sense the line, amplifier AC-BD,this will provide an output through Fdle and lead dffor operating relayRS.

Relay RS connects the output of amplifier AB-GH through Fde to theresolver R and the output of amplifier AB-CD through Fre and lead re tothe steering motor M. Motor M is then rotated in accordance with whetherthe total output of cells A+B at network ABl corresponds to the totaloutput of cells C+D at network CD to angularly align the head with thepattern edge. Simultaneously, since the pattern will overlie all ofeither cells G or H together with a portion of cell A and cell B, theoutput of network AB will be unbalanced from that of network GH, as theaxis 42 is displaced from the pattern edge, a displacement error signalis provided to lead de and through the resolver R to drive the X and Ymotors for aligning the direction of travel 16 with the pattern edgeindicated at 14. At that time the output of cells A+B equals G+Hequalizes and the X and Y motors simply operate under the selected speedsignals to follow the pattern edge in accordance with a change in outputfrom either cells A, B, C and D.

It will be appreciated that although triangular cell shapes are shownunder some circumstances, masks may be used on the photocells to providetriangular sensitive areas and by the use of mirrors the cells may belocated in other head positions than those shown.

The foregoing constitutes a description of improved line tracingapparatus whose inventive concepts are believed set forth in theaccompanying claims.

What is claimed is:

l. A photosensitive arrangement carried by a movable scanning head forcontrolling the position of said head relative a contour line definingeither a pattern edge or a drawing line, the improvement comprising afirst pair of photosensitive cells carried by said head with each cellhaving an equal light sensitive area of triangular configuration formovement with said head into a position overlapping said line, one celltriangular area defined by an isosceles triangle and the other celltriangular area defined by two right triangles each having a hypotenuseadjacent and substantially coextensiv'e with a respective one of theequal legs of said isosceles triangle, and means for projecting an imageof said'line on said cells in response to movement of said cells intosaid overlapping position whereby said cells provide equal outputsignals in response to the projected image of said line dividing eacharea into equal portions and unequal output signals in response to theprojected image of said line dividing each area into unequal portions.

2.- The photosensitive arrangement claimed in claim 1 in which said headis rotatable by one motor to maintain said head in a predeterminedangular position relative said line and said head is movedlongitudinally along said line by a pair of coordinatedrive motors, theimprovement comprising a second pair of said cells each having an areaof triangular configuration corresponding to a respective oneof saidfirst cells and said head has an axis of rotation lying between saidfirst and second pairs of cellsand along a line bisecting eachtriangular area, first means for combining the output signal from eachcell of said one pair with a signal from each respective cell of theother pair for determining the displacement of said line image from saidbisecting line, and second means for combining the output signal fromeach cell of said one pair with a signal from each respective other cellof the other pair for deriving a first signal corresponding to theangular orientation of said image relative said axis at a positionspaced from said axis along the direction of head movement.

3. In the arrangement claimed in claim 2, a pair of serially connectedresistors with one of said resistors connected to said means forcombining said signals to derive a first signal corresponding to theangular orientation, an amplifier having an input connected to the otherone of said resistors and an output connected to said one motor forrotating said head, normally ineffective means connected between saidresistors for reducing the signal applied to said amplifier from saidresistors for reducing the rate at which said one motor rotates saidhead, and manually operable means for rendering said ineffective meanseffective to reduce the signal applied from said resistors to saidamplifier input for reducing said rate of rotation.

4. In the arrangement claimed in claim 2, a third pair of cells eachhaving an area of triangular configuration corresponding to a respectiveone of said first and second pair of cells with said second pair ofcells spaced intermediate said first and third pair of cells, means forcombining the output signal of each cell of said first pair of cellswith the output signal of a cell of said third pair to derive a secondsignal corresponding to the angular orientation of said image relativesaid axis at a position spaced from said axis along the direction ofmovement, and manually operable means for connecting either said firstsignal or said second signal to said one motor for rotating said head inaccordance with the speed of said coordinate drive motors.

5. In the arrangement claimed in claim 2, an additional pair of cells ofequal area each spaced adjacent a respective end of said first cell pairin a direction transverse to said line image, means for combining theoutputs of said additional pair of cells with each other, means forcombining the outputs of said first pair of cells with each other, andmeans for combining the combined signals of said additional and firstpairs of cells for driving said coordinate motors in response to saidcontour line defining a pattern edge with one cell of said additionalpair of cells overlapping the pattern forming said edge.

6. In the arrangement claimed in claim 5, means for combining theoutputs of said second pair of cells with each other and with thecombined signal of said first pair of cells for determining the angularorientation of said pattern edge relative said axis.

7. In the arrangement claimed in claim 6, a start relay operated forinitiating control of said motors by said cells, manually operable meansfor selecting the combined outputs of said additional and first pair ofcells for operating said start relay in response to said contour linedefining a drawing line, and manually operable means for selecting thecombined outputs of each cell of said first pair with a respective cellof said second pair to determine line displacement for operating saidstart relay in response to said contour line defining a pattern edge.

8. In a scanning system of the type having a scanning head carrying aplurality of light sensitive cells for sensing the presence of a contourline, a steering head motor for rotating said head and cells in responseto a signal from said cells for enabling said cells to be posi- ,tionedin overlapping relationship to said contour line and at a predeterminedangle to said contour line from a position offset from said line forthereafter following said line at said angle, a pair of coordinate drivemotors for moving said head to and longitudinally along said line undercontrol of said steering head motor, an amplifier for amplifying thesignal derived from said cells for application to said steering motor, apair of serially connected resistors for transmitting said signal tosaid amplifier for enabling said amplifier to control said steeringmotor to rotate said head and cells to said predetermined angle inresponse to said cells being moved from said offset position to oneoverlapping position relative said line, normally ineffective meansconnected between said resistors for reducing the signal provided tosaid amplifier for reducing the rate of rotational movement of saidsteering head motor during movement of said head from said offsetposition into said one overlapping position, and manually operated meansoperated for rendering said normally ineffective means effective toreduce said signal during movement from said offset position to said oneoverlapping position and thereafter restored to render said signalreducing means ineffective.

t l i 4* 'l

1. A photosensitive arrangement carried by a movable scanning head forcontrolling the position of said head relative a contour line definingeither a pattern edge or a drawing line, the improvement comprising afirst pair of photosensitive cells carried by said head with each cellhaving an equal light sensitive area of triangular configuration formovement with said head into a position overlapping said line, one celltriangular area defined by an isosceles triangle and the other celltriangular area defined by two right triangles each having a hypotenuseadjacent and substantially coextensive with a respective one of theequal legs of said isosceles triangle, and means for projecting an imageof said line on said cells in response to movement of said celLs intosaid overlapping position whereby said cells provide equal outputsignals in response to the projected image of said line dividing eacharea into equal portions and unequal output signals in response to theprojected image of said line dividing each area into unequal portions.2. The photosensitive arrangement claimed in claim 1 in which said headis rotatable by one motor to maintain said head in a predeterminedangular position relative said line and said head is movedlongitudinally along said line by a pair of coordinate drive motors, theimprovement comprising a second pair of said cells each having an areaof triangular configuration corresponding to a respective one of saidfirst cells and said head has an axis of rotation lying between saidfirst and second pairs of cells and along a line bisecting eachtriangular area, first means for combining the output signal from eachcell of said one pair with a signal from each respective cell of theother pair for determining the displacement of said line image from saidbisecting line, and second means for combining the output signal fromeach cell of said one pair with a signal from each respective other cellof the other pair for deriving a first signal corresponding to theangular orientation of said image relative said axis at a positionspaced from said axis along the direction of head movement.
 3. In thearrangement claimed in claim 2, a pair of serially connected resistorswith one of said resistors connected to said means for combining saidsignals to derive a first signal corresponding to the angularorientation, an amplifier having an input connected to the other one ofsaid resistors and an output connected to said one motor for rotatingsaid head, normally ineffective means connected between said resistorsfor reducing the signal applied to said amplifier from said resistorsfor reducing the rate at which said one motor rotates said head, andmanually operable means for rendering said ineffective means effectiveto reduce the signal applied from said resistors to said amplifier inputfor reducing said rate of rotation.
 4. In the arrangement claimed inclaim 2, a third pair of cells each having an area of triangularconfiguration corresponding to a respective one of said first and secondpair of cells with said second pair of cells spaced intermediate saidfirst and third pair of cells, means for combining the output signal ofeach cell of said first pair of cells with the output signal of a cellof said third pair to derive a second signal corresponding to theangular orientation of said image relative said axis at a positionspaced from said axis along the direction of movement, and manuallyoperable means for connecting either said first signal or said secondsignal to said one motor for rotating said head in accordance with thespeed of said coordinate drive motors.
 5. In the arrangement claimed inclaim 2, an additional pair of cells of equal area each spaced adjacenta respective end of said first cell pair in a direction transverse tosaid line image, means for combining the outputs of said additional pairof cells with each other, means for combining the outputs of said firstpair of cells with each other, and means for combining the combinedsignals of said additional and first pairs of cells for driving saidcoordinate motors in response to said contour line defining a patternedge with one cell of said additional pair of cells overlapping thepattern forming said edge.
 6. In the arrangement claimed in claim 5,means for combining the outputs of said second pair of cells with eachother and with the combined signal of said first pair of cells fordetermining the angular orientation of said pattern edge relative saidaxis.
 7. In the arrangement claimed in claim 6, a start relay operatedfor initiating control of said motors by said cells, manually operablemeans for selecting the combined outputs of said additional and firstpair of cells for operating said start relay in response to saId contourline defining a drawing line, and manually operable means for selectingthe combined outputs of each cell of said first pair with a respectivecell of said second pair to determine line displacement for operatingsaid start relay in response to said contour line defining a patternedge.
 8. In a scanning system of the type having a scanning headcarrying a plurality of light sensitive cells for sensing the presenceof a contour line, a steering head motor for rotating said head andcells in response to a signal from said cells for enabling said cells tobe positioned in overlapping relationship to said contour line and at apredetermined angle to said contour line from a position offset fromsaid line for thereafter following said line at said angle, a pair ofcoordinate drive motors for moving said head to and longitudinally alongsaid line under control of said steering head motor, an amplifier foramplifying the signal derived from said cells for application to saidsteering motor, a pair of serially connected resistors for transmittingsaid signal to said amplifier for enabling said amplifier to controlsaid steering motor to rotate said head and cells to said predeterminedangle in response to said cells being moved from said offset position toone overlapping position relative said line, normally ineffective meansconnected between said resistors for reducing the signal provided tosaid amplifier for reducing the rate of rotational movement of saidsteering head motor during movement of said head from said offsetposition into said one overlapping position, and manually operated meansoperated for rendering said normally ineffective means effective toreduce said signal during movement from said offset position to said oneoverlapping position and thereafter restored to render said signalreducing means ineffective.